This invention relates generally to electronic electricity meters and, more particularly, to a low cost, high accuracy current conductor configuration for the electronic electricity meter for the primary current carrying conductors.
Power distribution systems include many electrical devices. Some of the electrical devices have current sensors for sensing current flow in a conductor. For example, power distribution systems generally include circuit breakers, electricity meters, and monitoring equipment. The accuracy of such current sensors is important, since inaccurate current sensing could lead to unnecessarily cutting-off power to a load and discrepancies in power metering, which are undesirable. Although known sensors provide acceptable results, it would be desirable to even further improve the sensing accuracy of current sensors and to reduce costs.
In addition to high accuracy and low cost, the size of current sensors often is important. For example, if products must be redesigned in order to incorporate a new current sensor, the cost of adding the new current sensor to the product can be very expensive. Preferably, any new current sensor is sized so that the sensor can be easily installed into existing units, such as meters and circuit breakers.
In addition, conductor configurations for electricity meters impose restrictions on current sensors. These restrictions are lightened appreciably if the conductors are designed specifically for the current sensor in use.
Accordingly, it would be desirable to provide a current sensor assembly that is accurate and of low cost. It would be further desirable to provide a current sensor that readily replaces existing current sensors and is of low profile. In addition, it would be desirable to provide a current sensor including conductors specifically designed for the particular application.
These and other objects may be attained by a current sensor assembly including a sensor coil, an electrostatic shield coil, a core, a housing, and a magnetic shield. The sensing coil, electrostatic shield coil, core, housing, and magnetic shield are of toroidal symmetry and are arranged coaxially about a pair of primary current conductors. The conductors can be either asymmetrical or symmetrical with respect to the geometric center of the remaining sensor assembly.
The core has the shape of a toroid and is of non-magnetic material. The sensor winding is wound over the toroidal core to form a toroid shaped winding. The electrostatic shield winding is then wound around the sensor winding. When assembled into the current sensor assembly, the core and windings are disposed around two conductors. AC currents to be measured flow in the conductors, creating an alternating magnetic flux in the core. This flux induces a voltage in the sensor winding which is connected to the input of an amplifier and an integrator.
The conductors can be either symmetrical with respect to each other or asymmetrical. In the asymmetrical case, the conductors pass side by side through an air space in the middle of the sensor such that the common middle of the line joining the center of the conductors is at the geometric center of the remaining toroidal assembly. In the symmetrical case, the center of the concentric conductor assembly is at the geometrical center of the remaining toroidal assembly.
The conductor configurations are used to fabricate a low cost, high accuracy current sensor using an air core. The current sensor detects the value of current flowing in the main conductors in a residential electronic meter accurately and at low cost to enable an overall low cost electronic meter. Although the present embodiment uses an air core, a core of high permeability material can also be used.